The present invention relates to an atmospheric pressure interface of a mass spectrometer, a mass spectrometer and a method of forming an atmospheric pressure interface of a mass spectrometer.
Mass spectrometers are known which comprise an atmospheric pressure interface. The atmospheric pressure interface comprises a removable outer gas cone and an inner sampling cone. The inner sampling cone is inserted within an ion block or sub-assembly which comprises a housing and which provides an interface between an ion source and the main housing of the mass spectrometer. The main housing of the mass spectrometer comprises several vacuum chambers and a mass analyser which is located in a downstream vacuum chamber. The outer gas cone is secured to the ion block or sub-assembly of the mass spectrometer using screws or allen bolts. The process of securing the outer gas cone to the ion block or sub-assembly of the mass spectrometer also secures the inner sampling cone in place.
Cone gas (e.g. nitrogen) is supplied to an annular region which is formed between the inner sampling cone and the outer gas cone. The cone gas flows out of the annular region to atmosphere through an aperture at the apex of the gas cone. Analyte ions generated by an ion source pass through the same aperture into the body of the ion block or sub-assembly i.e. in the opposite direction.
The cone gas helps to reduce the formation of undesired solvent cluster ions and solvent adduct ions and helps to keep the inner sampling cone (which includes a small gas limiting orifice) clean.
U.S. Pat. No. 5,793,039 (Oishi) discloses a conventional arrangement in which an outer cone is attached to a vacuum chamber by screws. An inner cone is detachably attached to a conical base by a clamp and screws.
GB 2288273 (Hu) discloses with reference to FIG. 3 a conventional arrangement in which an outer cone is secured to a mass spectrometer by screws.
US 2003/0189170 (Covey) discloses a mass spectrometer in which various elements are mounted and secured to the housing in a known manner.
WO 2009/137463 (Waters) discloses an ion source housing affixed on or about an opening of a high pressure region.
The conventional approach of securing an outer gas cone to an ion block or sub-assembly using screws or allen bolts suffers from the problem that in order to clean or replace the outer gas cone (or to access, clean or replace the inner sampling cone or other components) it is necessary for a user to use a tool such as a screwdriver or an allen key in order to unscrew the screws or allen bolts in order to detach the gas cone from the ion block.
The process of unscrewing and removing a conventional gas cone is problematic in that immediately after use the gas cone will be very hot and hence may be difficult for a user to handle. A user is exposed to the risk of suffering a burn from inadvertently touching the gas cone whilst unscrewing the gas cone from the ion block. Furthermore, once the gas cone has been unscrewed then there is an added risk that a user may accidentally drop the gas cone since it can be difficult to handle the gas cone particularly when it is very hot.
The use of screws or allen bolts to secure the gas cone to the ion block or sub-assembly of a mass spectrometer suffers from the problem that the screws or allen bolts will tend to seize up and will otherwise fail after a relatively short period of use since the screws or allen bolts are routinely subjected to harsh operating conditions. In particular, the screws or allen bolts are subjected to demanding temperature cycles and fluctuations as well as being exposed to harsh chemical fluids and heated gases. The harsh operating conditions reduces the effective lifetime of the screws or allen bolts.
Another problem with the conventional arrangement is that a user may inadvertently overtighten the screws or allen bolts which can damage the threads. Alternatively, a user may insufficiently tighten the screws or allen bolts which can result in gas and vacuum leakage and general sub-optimal performance.
It will be appreciated, therefore, that there are a number of significant problems with the conventional arrangement wherein an outer gas cone is secured to an ion block or sub-assembly using screws or allen bolts.
It is desired to provide an improved mass spectrometer.